Factors Associated with Prevalent Self-Reported Arthritis and Other Rheumatic Conditions -- United States, 1989-1991

Arthritis and other rheumatic conditions are among the most prevalent diseases in the United States, particularly for women and some racial/ethnic groups (1-3). In 1992, arthritis was the leading cause of disability and was associated with total direct and indirect costs of $64.8 billion (4); projections indicate that by 2020, arthritis will affect 59.4 million (18.2%) persons in the United States (1). Previous reports have documented marked differences in the prevalence rates of arthritis by age, sex, race, ethnicity, education, and body mass index (BMI) (1-3). To examine the relative importance of these factors, CDC used data from the 1989-1991 National Health Interview Survey (NHIS) and a multivariate model to estimate the independent effect of each factor on self-reported arthritis. This report summarizes the results of that analysis, which indicate that a higher risk for arthritis is associated with older age, overweight, or obesity and that a lower risk is associated with being Asian/Pacific Islander or Hispanic or with having a higher education level.

The NHIS is an annual national probability sample of the U.S. civilian, noninstitutionalized population (5). Estimates of the prevalence of arthritis were based on a one-sixth random sample (n=59,289) of respondents who answered questions about the presence of any musculoskeletal condition during the preceding 12 months and provided details about these conditions. Each condition was assigned a code from the International Classification of Diseases, Ninth Revision (ICD-9). This analysis used the definition of arthritis, which included arthritis and other rheumatic conditions, developed by the National Arthritis Data Workgroup (1) *. The final sample of 41,919 excluded persons aged less than 18 years (n=16,488), for whom self-reported height and weight were not asked, and persons aged greater than or equal to 18 years for whom such data were missing (n=882).

Multivariate logistic regression was used to assess the relation between self-reported arthritis and age, race, ethnicity, education, and BMI. Previous studies have documented that each of these variables is associated with arthritis (1-3,6-8). Because stratified analyses suggested that the effect of BMI on arthritis differed by sex, the model was applied separately to men and women. For this analysis, BMI (weight {kg}/height {m}2) was divided into four categories: underweight (BMI less than 20), normal weight (20 less than or equal to BMI less than 25), overweight (25 less than or equal to BMI less than 30), and obese (BMI greater than or equal to 30) (9). SUDAAN was used to weight observations and to account for the complex sampling design.

Of the 41,919 persons surveyed, 8706 (21%) reported having arthritis. Older age was the strongest overall predictor for self-reported arthritis (Table_1). Among women, risk for arthritis varied directly with BMI. Among men, the risk was higher among those with greater BMI (odds ratio {OR}=1.3 {95% confidence interval (CI)=1.1-1.4} for overweight, OR=1.7 {95% CI=1.5-2.0} for obese), and those who were underweight (OR=1.4 {95% CI=1.0-1.8}), could cause chronic weight loss (e.g., infections and neoplasms). Risk for arthritis was similar by race for all groups except Asians/Pacific Islanders (OR=0.6 {95% CI=0.4-0.9}), and by ethnicity, was lower among Hispanics. For men, risk was lower for those who were college graduates (OR=0.8 {95% CI=0.7-1.0}) or who attended graduate school (OR=0.7 {95% CI=0.6-0.9}). Models using different BMI categories and models run without proxy-reported observations yielded similar findings.

Reported by: Dept of Epidemiology, School of Public Health, Univ of North Carolina, Chapel Hill. K Johnston-Davis, Association of Schools of Public Health, Washington, DC. Div of Adult and Community Health, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: The category of arthritis and other rheumatic conditions comprises several specific diseases associated with a spectrum of etiologies (Table_2). However, the epidemiology of most of these conditions -- including incidence and prevalence estimates -- has notbeen well characterized. In the United States, the most common types of arthritis include osteoarthritis and rheumatoid arthritis.

The findings of this analysis indicate that, even when adjusted for other factors, risk for arthritis is higher among persons who are overweight or obese or of older age. In addition, this report documents the low risk for arthritis among Asians/Pacific Islanders and Hispanics and among men with higher education. Although NHIS could not determine whether respondents were overweight or obese before or after the onset of arthritis, previous studies have documented that overweight or obesity are risk factors for osteoarthritis of the knee (6-8). The low risk for arthritis among Asians/Pacific Islanders and Hispanics persisted after adjustment for age, BMI, and education. These race/ethnicity-specific associations may reflect variations in cultural thresholds for reporting arthritis, risk factors (e.g., joint injury, occupations involving knee bending, and low socioeconomic status), or genetic determinants (e.g., rheumatoid arthritis). The finding of increased risk for arthritis among underweight men has not been reported previously and may reflect differences in self-reporting of arthritis, history of previous joint injury, or presence of other severe chronic conditions.

The findings in this report are subject to at least two limitations. First, the self-reported information comprising NHIS has not been validated; however, because only 84% of persons reporting arthritis have ever sought care from a physician for evaluation or treatment of this condition, these findings may reflect the prevalence of rheumatic conditions more accurately than estimates based on reviews of clinical databases (1). Second, previous traumatic injury to a joint -- a recognized risk factor for osteoarthritis -- was not included in NHIS; therefore, differences in the occurrence of this risk factor may have accounted for some observed associations.

Overweight is a modifiable characteristic that is an important risk factor for knee osteoarthritis (Table_2) and as either a risk factor for or adverse consequence of other types of arthritis. interventions for preventing excess weight gain. In addition, further characteristics of the epidemiology of and risk factors for specific types of arthritis are necessary to further reduce the public health impact of arthritis.

References

1. CDC. Arthritis prevalence and activity limitations -- United States, 1990. MMWR 1994;43:433-8.

2. CDC. Prevalence and impact of arthritis among women -- United States, 1989-1991. MMWR 1995;44:329-34.

3. CDC. Prevalence and impact of arthritis by race and ethnicity -- United States, 1989-1991. MMWR 1996;45:373-8.

4. Yelin E, Callahan LF. The economic cost and social and psychological impact of musculoskeletal conditions. Arthritis Rheum 1995;38:1351-62.

5. Massey JT, Moore TF, Parsons VL, Tadros W. Design and estimation for the National Health Interview Survey, 1985-94. Vital Health Stat 1989;2:1-4.

6. Felson, DT. Weight and osteoarthritis. J Rheumatol 1995;(suppl 43):7-9.

7. Anderson JJ, Felson DT. Factors associated with osteoarthritis of the knee in the first National Health and Nutrition Examination Survey (NHANES I): evidence for an association with overweight, race, and physical demands of work. Am J Epidemiol 1988;128:179-89.

8. Felson, DT. Epidemiology of hip and knee osteoarthritis. Epidemiol Rev 1988;10:1-28.

9. Verbrugge LM, Gates DM, Ike RW. Risk factors for disability among U.S. adults with arthritis. J Clin Epidemiol 1991;44:167-82.

10. Lawrence RC, Hochberg MC, Kelsey JL, et al. Estimates of the prevalence of selected arthritic and musculoskeletal diseases in the United States. J Rheumatol 1989;16:427-41.

• International Classification of Diseases, Ninth Revision, Clinical Modification, codes 95.6, 95.7, 98.5, 99.3, 136.1, 274, 277.2, 287.0, 344.6, 353.0, 354.0, 355.5, 357.1, 390, 391, 437.4, 433.0, 446, 447.6, 696.0, 710 716, 719.0, 719.2 719.9, 720 721, 725 727, 728.0 728.3, 728.6 728.9, 729.0 729.1, and 729.4.

TABLE 1. Factors associated with self-reported arthritis and other
rheumatic conditions among persons aged >=18 years in a multivariate
model, by sex -- National Health Interview Survey, United States, 1989-1991 *
================================================================================
                         Men (n=19,534)            Women (n=22,385)
                     ------------------------    -----------------------
Factors              Odds ratio +  (95% CI &)    Odds ratio  (95% CI)
--------------------------------------------------------------------------------
Body Mass Index @
  Underweight            1.4      ( 1.0- 1.8)        0.9    ( 0.8- 1.0)
  Normal weight          1.0        referent         1.0      referent
  Overweight             1.3      ( 1.1- 1.4)        1.3    ( 1.2- 1.5)
  Obese                  1.7      ( 1.5- 2.0)        1.5    ( 1.3- 1.7)

Age Group (yrs)
  18-24                  1.0        referent         1.0      referent
  25-34                  2.3      ( 1.6- 3.4)        2.0    ( 1.5- 2.6)
  35-44                  4.9      ( 3.4- 7.0)        3.4    ( 2.5- 4.7)
  45-54                  8.1      ( 5.6-11.6)        7.2    ( 5.4- 9.7)
  55-64                 14.4      (10.2-20.5)       10.6    ( 8.0-14.1)
  65-74                 16.0      (11.0-23.3)       12.9    ( 9.5-17.5)
  75-84                 18.5      (12.3-27.9)       16.0    (11.9-21.5)
   >=85                 16.0      ( 8.6-29.5)       12.9    ( 9.0-18.6)

Race
  White                  1.0        referent         1.0      referent
  Black                  0.9      ( 0.7- 1.1)        0.9    ( 0.8- 1.1)
  American Indian/
   Alaskan Native        1.6      ( 1.0- 2.6)        1.2    ( 0.7- 2.1)
  Asian/Pacific Islander 0.6      ( 0.4- 0.9)        0.6    ( 0.4- 1.0)
  Other                  1.0      ( 0.6- 1.6)        1.1    ( 0.7- 1.5)

Ethnicity
  Hispanic               0.6      ( 0.5- 0.8)        0.7    ( 0.5- 0.8)
  Non-Hispanic           1.0        referent         1.0      referent

Education
  Less than high school  1.1     ( 1.0- 1.4)         1.0    ( 0.9- 1.2)
  Some high school       1.1     ( 0.9- 1.3)         1.2    ( 1.1- 1.4)
  High school graduate   1.0       referent          1.0      referent
  Some college           1.0     ( 0.9- 1.2)         1.1    ( 1.0- 1.2)
  College graduate       0.8     ( 0.7- 1.0)         0.9    ( 0.7- 1.0)
  Graduate school        0.7     ( 0.6- 0.9)         0.9    ( 0.8- 1.1)
--------------------------------------------------------------------------------
* Race and Hispanic ethnicity (not mutually exclusive terms) are based on
  the respondent's description of his or her background. Arthritis is defined
  using the National Arthritis Data Workgroup's definition, which is based
  on the International Classification of Diseases, Ninth Revision, Clinical
  Modification, codes 95.6, 95.7, 98.5, 99.3, 136.1, 274, 277.2, 287.0,
  344.6, 353.0, 354.0, 355.5, 357.1, 390, 391, 437.4, 433.0, 446, 447.6,
  696.0, 710-716, 719.0, 719.2-719.9, 720-721, 725-727, 728.0-728.3,
  728.6-728.9, 729.0-729.1, and 729.4.
+ Logistic regression models run separately for men and women.
& Confidence interval.
@ Body mass index (BMI)=weight (kg)/height (m)2. Underweight=BMI<20;
  normal=20<=BMI<25.0; overweight=25<=BMI<30; obese=BMI>=30.
================================================================================

TABLE 2. Selected types and characteristics of arthritis and other rheumatic conditions *
==============================================================================================
                                           Estimated 1985
Type                  Examples               prevalence +     Risk factors
----------------------------------------------------------------------------------------------
Degenerative          Osteoarthritis         15,800,000       Increasing age, female;
                                                              joint trauma; repetitive use;
                                                              overweight &

Systemic autoimmune   Rheumatoid arthritis    2,100,000       Increasing age, female
                      Systemic lupus            131,000       Female; black
                        erythematosus

Seronegative          Ankylosing spondylitis    318,000       Male; HLA-B27 gene
 spondylo-
 arthropathies

Infectious            Gonococcal arthritis       30,000       Sexually active
                      Lyme arthritis               NA @       Tick bite in endemic area

Metabolic/Endocrine   Gout                    1,000,000       Increasing age; male

Rheumatism            Bursitis, tendinitis           NA       Overuse
                      Fibromyalgia                   NA       Adult; female
----------------------------------------------------------------------------------------------
* Excludes other musculoskeletal conditions such as tumors, bone disorders, fractures, and
  back and neck disorders.
+ Reference 10.
& For knee osteoarthritis only.
@ Not available.
==============================================================================================

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